Timepiece having vibration isolation means

ABSTRACT

A DRIVE MECHANISM FOR USE WITH A TIMEPIECE HAVING A HOUSING, THE DRIVE MECHANISM INCLUDING A FRAME, AN OUTPUT MEMBER MOUNTED ON THE FRAME, VIBRATORY ELEMENT DRIVINGLY CONNECTED TO THE OUTPUT MEMBER AND A VIBRATION ISOLATING MOUNTING UNIT SECURING THE FRAME TO THE TIMEPIECE HOUSING, THE VIBRATION ISOLATING MOUNTING UNIT HAVING A CHARACTERISTIC NATURAL FREQUENCY BELOW THAT OF THE VIBRATORY ELEMENT, AND HAVING FREEDOM OF MOVEMENT IN THE DIRECTION OF A COMPONENT OF VIBRATORY MOVEMENT OF THE FRAME AT A POSITION THEREON WHERE THE MOUNTING UNIT IS ATTACHED.

1971 P. A. SIDELL ET AL 3,552,116

TIMEPIECE HAVING VIBRATION. ISOLATION MEANS Filed Aug. 5, 1967 F/G. I

F/G. Z

F/G4 Z5 Z5 Z0 g7 I N VIOL N TURS PHILIP A. SIDELL 55 CECIL F. CLIFFORD ATTORNEYS United States Patent 3,552,116 TIMEPIECE HAVING VIBRATION ISOLATION MEANS Philip Alden Sidell, West Hartford, Conn., and Cecil Frank Clifford, Somerset, England, assignors to The Ingraham Company, Bristol, Conn., a corporation of Connecticut Filed Aug. 3-, 1967, Ser. No. 664,590 Claims priority, application Great Britain, Aug. 17, 1966, 36,856/ 66 Int. Cl. G04c 3/00 US. Cl. S823 13 Claims ABSTRACT OF THE DISCLOSURE A drive mechanism for use with a timepiece having a housing, the drive mechanism including a frame, an output member mounted on the frame, a vibratory element drivingly connected to the output member and a vibration isolating mounting unit securing the frame to the timepiece housing, the vibration isolating mounting unit having a characteristic natural frequency below that of the vibratory element, and having freedom of movement in the direction of a component of vibratory movement of the frame at a position thereon where the mounting unit is attached.

This invention generally relates to the control of deleterious side effects resulting from the use of vibratory elements in devices such as clock motors and escapements and is more particularly related to the provision of an improved mounting for such devices.

Of particular concern in the construction of timepieces is the provision of a time accurate drive mechanism for the clock hands and which drive mechanism is also small in size, efficient and quiet in operation. The development of electromagnetic drive mechanisms particularly suited for use in so-called cordless or battery-operated clocks has emphasized the aforementioned desirable characteristics and has resulted in the commercial development of drive mechanisms utilizing vibratory elements. A typical motor utilizing an electromagnetically driven vibratory drive mechanism is disclosed and claimed in C. F. Clifford et al. Pat. No. 2,606,222. A typical magnetic escapement using a vibratory element and suitable for timepieces is disclosed and claimed in C. F. Clifford Pat. No. 2,571,085. Heretofore an inherent deficiency in such a drive mechanism using a vibratory element is the generation of noise which may be so objectionable as to make the product commercially unsuitable for many applications.

It is, therefore, a principal object of this invention to provide a timepiece having the accuracy and efliciency but not the objectionable noise normally associated with a drive mechanism using one or more vibratory elements.

It is an additional object of this invention to provide an improved mounting for a vibratory element timepiece drive mechanism which substantially reduces unwanted noise while preserving the accuracy, efficiency and low power drain characteristics of such mechanisms.

Other objects will be in part obvious and in part pointed out more in detail hereinafter.

The invention accordingly consists in the features of construction, combination of elements and arrangement of parts which will be exemplified in the construction hereafter set forth in the following detailed description and accompanying drawing of an illustrative application of the invention.

In the drawing:

FIG. 1 is a front elevation view of a shelf clock embodying the present invention;

FIG. 2 is a rear elevation view of the clock of FIG. 1

with the rear access door open to expose the drive mechanism;

FIG. 3 is an enlarged front elevation view, partially cut away, of the drive mechanism illustrated in FIG. 2; and

FIG. 4 is an enlarged cross section view taken along the line 44 of FIG. 2.

By way of general explanation, it has long been realized that a vibratory element such as a tuning fork when driven at its resonant frequency constitutes a very accurate time base from which to control the accuracy of a timepiece drive mechanism and uses for such a tuning fork concept have been made not only as an escapement to control the accuracy of a mechanism having a separate power source but also in the motor or drive source itself. Unfortunately, such tuning fork mechanisms leak vibratory energy which often creates objectionable noise levels of operation for the drive mechanism. The unwanted vibration of the drive mechanism is believed to come principally from such factors as imprecise mounting of the tuning fork or other vibratory elements at other than a node point, variation in the output energy of the vibratory element which variations are magnetically coupled to the mounting frame and the drive of the vibratory element (normally an electromagnetic drive) which experiences reaction-type vibration.

While improvement in manufacturing techniques can often reduce certain of the sources of unwanted noise vibration from such a drive mechanism, the fact that a particular drive mechanism may find application in a wide variety of timepieces creates the need for a low-cost, universally applicable solution to the noise problem.

Attempts hitherto made in solving this problem have involved efforts to reduce or eliminate the spurious vibrations through the use of vibration absorption devices. Such attempts have been ineffective not only because absorption devices are inherently high hysteresis devices having high mechanical losses in vibration likely to transmit more noise vibration than is absorbed, but also because absorption devices create an additional and unwanted load for the vibratory member in the drive system.

In accordance with the present invention, the unwanted noise vibrations are treated so as to isolate these vibrations from the typical timepiece housing which generally renders such vibrations sonically apparent or conducts them to other environmental structures to produce unwanted noise. Moreover, the isolation approach permits creation of a predetermined set of environmental conditions in which the vibratory drive is to operate.

Turning now to the drawing wherein FIGS. 1 and 2 illustrate a typical shelf clock embodying a vibratory drive mechanism, such a typical clock comprises a clock face 1 which cooperates with a pair of clock hands 2, 3 to function as a time indicator, the clock hands being driven from a drive mechanism generally designated 5. In a typical clock, the drive mechanism can be considerably smaller than the decorative timepiece enclosure 6, such that opening of the rear door 7 provides access not only for installation of the drive mechanism 5 but also for setting of the clock as by the convention control member 8.

The drive mechanism 5 has been conveniently and somewhat schematically illustrated as an electric motor of the type disclosed in C. F. Clifford et al. Pat. No. 2,606,- 222. Such a motor has an electromagnetically operated coil 10 energized from a battery source 11 to excite reed 9 supported at one end by the frame 12 and carrying a magnet 13 which cooperates with a rotor 14 to drive this rotor about its axis 15 in a manner more fully described in the aforementioned patent. A pinion 16 carried by the rotor cooperates with a gear train generally designated 17 to rotate the coaxial shafts 18 to which the clock hands are affixed. The entire drive mechanism is conveniently carried on a frame member 20, which frame member is shown as being a generally flat, rectangular member and which also supports the battery and provides a convenient subassembly, often referred to in the trade as a clock fit-up or movement suitable for use in a wide variety of timepiece housings. The entire mechanism is suitably enclosed in a cover 21 secured to the frame.

The foregoing structure is largely of conventional design to illustrate typical clock movement which when affixed to the clock housing 6 transmits thereto a portion of the vibratory energy associated with the vibrating reed, it being understood, of course, that such a reed can be replaced with a tuning fork conventionally driven from an electromagnetic source without departing from the present invention. Under such conditions, the clock housing often functions as a sounding board to amplify such vibratory energy to objectionable sonic levels.

In accordance with the present invention, the frame 20 is secured to the housing of the timepiece through use of three identical vibration isolating mountings generally designated 25, the details of which are most clearly seen in FIG. 4. For convenience of mounting, there is provided a base plate 26, which base plate is isolated from the frame 29 and can be secured directly to the timepiece housing as by the screws 40 and best seen in FIG. 2.

In determining the characteristics of the isolating mounting shown in FIG. 4, it has been ascertained that the isolating structure must be such as to create minimum energy loss, thereby to minimize the load placed upon the vibratory element 9. Minimizing this load is particularly important in battery-operated clock movements wherein the available energy is severely limited and accuracy of the drive mechanism can be seriously affected by premature reduction of the magnitude of the available drive energy.

In the preferred embodiment illustrated in FIG. 4, the isolator comprises a metallic coil spring 27 whose convolutions are secured at one end to the frame 20 and at the other end to the base 26, e.g., by suitable tangs 38 shown integrally formed thereon (or if desired on the timepiece housing), with each isolator being provided on peripheral portions of the frame 20 with its spring 27 positioned in its entirety outside the plane of the frame 20. A metallic coil spring is utilized because of its extremely low mechanical loss (energy dissipation) when vibrating and because it has been determined that the isolator must provide freedom of movement of the frame 20 at least in the direction of the vibratory energy vector at the point where the isolator is secured to the frame 20. It has been found that a coil spring, because it offers freedom of movement in all directions, is a preferred construction.

To further minimize vibratory energy transmission, it is important that the resonant frequency 12 of the vibration isolator be substantially below the frequency of vibration a of the vibratory system including the reed 9.

Utilizing the fundamental relationship of described in the text, Fundamentals of Vibration Analysis, N. O. Myklestad, Ph.D. (McGraw-Hill Book Company, Inc., 1956, p. 16) (where 6st is the static deflection of a spring isolator, g is the acceleration due to gravity, and f is the natural frequency of vibration of the spring) and assuming a natural frequency of b cycles per second, the static deflection of the desired springs is determined and, knowing the mass of the system to be supported, the desired physical parameters of the springs can be determined realizing that in the illustrated embodiment, the entire mass is supported by the three such springs. It must be realized that the maximum static deflection to be permitted is determined not only so as to preclude vibration conducting contact between the frame 20 and the base plate 26, but also to insure freedom of movement of the clock hands relative to the clock housing. It is, therefore, seen that knowing the frequency of vibration of the vibratory system and assuming a resonant frequency for the isolating springs 27 sufliciently below such frequency, a static deflection can be computed so as to determine the exact spring parameters. If the static deflection based upon the assumed frequency is too great, the other frequencies within the broad range below the frequency of the vibratory system can be tried.

Of further interest in FIG. 4 is the snubber construction which permits the spring 27 to have the desired softness within the expected range of movement to provide effective isolation while at the same time providing mechanical limits to preclude damage to clock hands, etc. during movement of the timepiece. The specific arrangement illustrated utilizes a threaded member 30 received within a threaded boss 31 provided on the frame, which threaded member is provided with a stop member 32 whose inner shoulder 33 traps the inner convolution 34 of the spring 27 for movement with the frame 2.0. Slotted head 35 is larger than the aperture 36 provided in base 26 so as to act as a stop to limit travel of the frame 20 away from the base 26.

It is to be understood that other low loss mechanical vibration isolators can be used instead of a metallic coil spring. Each of the alternative forms of an isolator must, however, provide the desired degree of freedom in the direction of vibratory movement at the point on the frame I where it is attached.

From the foregoing description, it will be appreciated that we have discovered that proper isolation of the vibratory system not only substantially reduces unwanted noise generation but also improves the operation of the drive system by providing controlled conditions in which it is to operate no matter what type of housing it is used with.

As will be apparent to persons skilled in the art, various modifications and adaptations of the structure above described will become readily apparent without departure from the teachings of the present invention.

The embodiments of the invention in which an exclusive property of privilege is claimed are defined as follows:

1. A low noise drive mechanism for timepieces suitable for mounting in a timepiece housing and comprising a frame, at least one output member mounted on said frame for driving a time indicator, means on said frame for driving said output member and including a vibratory element having a characteristic operating frequency of vibration, said vibratory element imparting a vibratory movement to said frame during said driving, and vibration isolating mounting means for securing said frame in the timepiece housing, the entire mass of the frame and components thereon being supported by said vibration isolating mounting means, said vibration isolating mounting means having a characteristic natural frequency that is below that of the characteristic frequency of the vibratory element and having at least'one direction of freedom of movement coextensive with the direction of the component of vibratory movement of the frame at the position wherein said mounting means is secured to said frame.

2. The low noise drive mechanism of claim 1 wherein said vibration isolating mounting means includes a metal coil spring and stop members to limit expansion of the spring.

3. The low noise drive mechanism of claim 1 wherein said frame is a generally flat member, and wherein said vibration isolating mounting means is secured between said frame and the timepiece housing and includes a metal spring secured therebetween with said spring being positioned in its entirety outside the plane of said frame and supporting the latter in spaced assembled relation to the timepiece housing.

4. The low noise drive mechanism of claim 1 wherein said vibration isolating mounting means includes a plurality of springs having low mechanical loss in vibration and a static deflection under the Weight of the drive mechanism permitting operative connection of said output member to the time indicator.

.5. The low noise drive mechanism of claim 2 wherein said metal spring is a coil spring having freedom of movement in a direction parallel to the direction of a component of vibratory movement.

6. A low noise drive mechanism for timepieces suitable for mounting in a timepiece housing and comprising a generally flat frame, at least one output member mounted on said frame for driving a time indicator, means on said frame for driving said output member and including a vibratory element having a characteristic operating frequency of vibration, said vibratory element imparting a vibratory movement to said frame during said driving, and vibration isolating mounting means including a metal coil spring cantilever mounted on the frame and secured between the frame and the timepiece housing for securing the frame therein, the entire mass of the frame and components thereon being supported by said vibration isolating mounting means, said vibration isolating mounting means having a characteristic natural frequency that is below that of the characteristic frequency of the vibratory element and having at least one direction of freedom of movement coextensive with the direction of the component of vibratory movement of the frame at the position wherein said mounting means is secured to said frame, the spring being positioned in its entirety outside the plane of said frame and supporting the latter in spaced assembled relation to the timepiece housing and having freedom of movement in the direction of the component of vibratory movement thereof at the position wherein the spring is cantilever mounted to the frame.

7. A low noise drive mechanism for timepieces suitable for mounting in a timepiece housing and comprising a generally fiat frame having a threaded boss formed therein, at least one output member mounted on said frame for driving a time indicator, means on said frame for driving said output member and including a vibratory element having a characteristic operating frequency of vibration, said vibratory element imparting a vibratory movement to said frame during said driving, and vibration isolating mounting means secured between said frame and the timepiece housing for securing said frame therein, said vibra tion isolating mounting means having a characteristic natural frequency that is below that of the characteristic frequency of the vibratory element and having at least one direction of freedom of movement coextensive with the direction of the component of vibratory movement of the frame at the position wherein said mounting means is secured to said frame, said mounting means having a metal spring secured between the frame and timepiece housing with said spring being positioned in its entirety outside the plane of said frame and supporting the latter in spaced assembled relation to the timepiece housing, and a threaded member received in said threaded boss of the frame, said threaded member being provided with a stop member having an inner shoulder which traps an inner convolution of said spring for movement with said frame, said threaded member having a free end formed with a slotted head which is larger than an aperture in a base plate secured to the timepiece housing through which said threaded member passes so as to limit travel of said frame away from the base plate.

8. The low noise drive mechanism of claim 4 wherein each of the springs in conjunction with its share of the total inertia of the movement has a characteristic natural frequency which is below the characteristic natural frequency of the vibratory element.

9. A low noise drive mechanism for timepieces suitable for mounting in a timepiece housing comprising a frame,

at least one output shaft journaled on said frame for drive connection to a timing indicator; means on said frame for rotating said output shaft including a vibratory element having a characteristic frequency of vibration, a rotor mounted adjacent said vibratory element, means magnetically coupling the movement of said vibratory element to said rotor thereby to effect controlled rotation thereof, electromagnetic drive means for said vibratory element for maintaining continued vibration thereof at its characteristic frequency and a gear train for transmitting rotation of said rotor to said output shaft; and vibration isolating means for securing said frame in the timepiece housing, said last named means including a plurality of springs of low mechanical hysteresis, the entire mass of said frame being supported by said springs under normal operating conditions when secured in a timepiece housing, each of said springs having a characteristic natural frequency that is below the characteristic natural frequency of the vibratory element.

10. The low noise drive mechanism of claim 8 wherein each of the said plurality of springs is an identical metal coil spring having freedom of movement in a direction parallel to the direction of a component of vibratory movement.

11. A low noise drive mechanism for timepieces suitable for mounting in a timepiece housing and comprising a frame, at least one output member mounted on said frame for driving a time indicator, means on said frame for driving said output member and including a vibratory element having a characteristic operating frequency of vibration, said vibratory element imparting a vibratory movement to said frame during said driving, and vibration isolating mounting means for securing said frame in the timepiece housing and including coil spring means secured between said frame and said timepiece housing, the entire mass of the frame and components thereon being supported by said coil spring means, said coil spring means having a characteristic natural frequency that is below that of the characteristic frequency of the vibratory element and providing freedom of movement of the frame in a direction parallel to the direction of a component of vibratory movement of the frame at the position wherein said mounting means is secured'to said frame, and said vibration isolating mounting means further including stop members for limiting expansion of said coil spring means.

12. The low noise drive mechanism of claim 11 further including a threaded member, one of the frame and timepiece housing members being threadably secured to one end of the threaded member, the other of the frame and timepiece housing members receiving an opposite end of the threaded member in spaced isolated relation thereto and providing said freedom of movement of the frame.

13. The loW noise drive mechanism of claim 12 wherein the stop members are provided on said threaded member for limiting expansion of said coil spring means.

References Cited UNITED STATES PATENTS 2,491,453 12/1949 Knobel 58-52 2,900,786 8/1959 Hetzel 58-23TF 3,198,324 8/1965 Kallenbach et al. 24820 RICHARD B. WILKINSON, Primary Examiner E. C. SIMMONS, Assistant Examiner US. Cl. X.R. 58-56; 248--114 

